Merge release/1.0 (SAFETY-78, #154) into opt11-p4-solar-forecast

Conflicts: modetrade.decide() takes both the day plan (targets) and
SAFETY-78's draining flag; the Why line keeps SAFETY-78's other_cycle
ahead of the plan's word (test added).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

goodwe_controller/DOCS.md

@@ -552,6 +552,7 @@ With battery modes on, these choices replace the *Charging and selling on price*
 - The peak limit, the safety stops and the monthly cycle come before a battery's mode.
 - A grid charge is sized so the 15-minute period stays under the peak limit less its margin (`peak_margin_w`). It starts only at 500 W or more. Once the peak limit stops it, it stays off for the rest of that 15-minute period.
 - While one battery charges from the grid, the others rest, and the house uses the grid.
+- While one battery empties for its monthly cycle, no battery charges from the grid.
 - A battery that refuses to charge or give power takes no part in a run in that direction.
 
 **In Home Assistant.** With MQTT set up, each battery also gets a *Mode* list and a *Use* switch, for example `select.goodwe_inverter_a_mode` and `switch.goodwe_inverter_a_use`. They do the same as the Batteries screen. Turn battery modes off and restart, and they are removed.
@@ -1660,6 +1661,10 @@ under `peak_cap_w`, and if the forecast goes over the cap the charge-only clamp
 is dropped so the battery can shave the peak instead. Money outranks the
 maintenance schedule.
 
+With two or more batteries, the one being emptied gives its drain rate and the
+others only add power when the house needs more; none charges while it drains
+(SAFETY-78). Below the drain rate the rest is exported, as with one battery.
+
 #### Capacity-tariff exposure of the grid-following loop
 
 ⚠️ **This section described the exposure BEFORE SAFETY-07. The loop is now